The invention concerns a knife holder for a microtome having a blade guard constituted as a pivotable bow, wherein, in its protective position, the blade guard is disposed on the side of the knife facing away from the sample at a distance from the cutting edge of the knife such that access to the cutting edge is not possible, and wherein the knife holder is held in a guideway on a support element in such way that it can be laterally slid and fixed so as to deploy different regions of the cutting edge during the sectioning operation.
Microtomes are used to make thin sections of the most varied specimens in medicine, biology, material research, and quality control of technical substances in a thickness range from approx. 0.1 μM to 100 μm. Biological and medical specimens are frequently embedded in more solid materials (e.g. paraffin, synthetic resin) to provide the stability necessary for sectioning.
The sections are produced either as single sections or as continuous series of sections. Thin sections are prepared using knives of different shapes and attributes. The known types include steel knives made of selected tool steels that are manufactured by various grinding methods. In addition to these resharpenable solid knives, disposable blades are used that are classified into low-profile blades and high-profile blades and are replaced with new blades once they have exceeded their useful life (usefulness for sectioning). Glass knives and diamond knives are also used for special applications.
Depending on the type of microtome, the knife is either moved along a stationary specimen in a sled (classic sled microtome) or the specimen is moved along the stationary knife by means of a specimen sled (rotary microtome). Stationary means that the knife is completely fixed during the entire sectioning operation. Of course, the knife can be placed in different positions in front of the sample between cuts, as is required for approximate positioning of the knife in front of the sample, advancement of the knife during sectioning, and also for lateral movement of the knife to make use of the entire cutting region of the knife.
In the case of rotary microtomes, the knife is usually held firm by clamping into a knife holder, wherein the knife is placed against the base body of the knife holder in such a way that the cutting edge protrudes beyond this base body and is clamped firmly thereon by means of a clamping plate. This is usually achieved using a simple clamping lever that either fixes or releases the knife.
The knife holder is usually on a support element constituted as a segment arc that is used to adjust the angle at which the knife cuts through the sample. The segment arc is positioned with its arc-shaped underside in a correspondingly constituted depression in the base support below it, which is in a guideway in front of the specimen holder and permits movement toward and away from the sample. This enables the knife to be put into position and advanced.
To be able to adjust the lateral position of the knife with respect to the sample in order to deploy other regions of the cutting edge, a guideway on the segment arc is used in which the knife holder can be moved laterally with respect to the sample.
To secure the selected position of the knife for the sectioning operation, the knife holder must be fixed, which can be achieved, for example, by means of a clamping mechanism. Such a mechanism is usually a simple clamping lever that either fixes or releases the knife holder in its position in the guideway.
The primary purpose of the knife holders used is to clamp the knife stably, i.e. with as little vibration as possible, so as to achieve a thin section of the necessary quality, i.e. without damaging or distorting the tissue. An essential property of all knives used is that the cutting edge is sharp enough for the specimen to be sectioned and for the selected section thickness in order to achieve a clean initial cut followed by clean parting of the tissue. It is the task of the user to monitor the progress of sectioning, for which purpose a free view of the cutting edge in the region of the sample is necessary during sectioning. The section or series of sections produced is deposited over the cutting edge on the knife cutting edge or on the clamping plate of the knife holder, depending on the specimen size, and must be removed from there. This is achieved, for example, using a fine brush or a pair of tweezers.
For the user of the microtome, all handling of the device therefore involves a danger of incurring cut wounds to the hand. In the case of rotary microtomes with a stationary knife, blade guard mechanisms are usually provided that cover the cutting edge during preparatory work, in work breaks, or during idle times. For this purpose, these guard mechanisms are either freely placed onto the knife or they are fixed to the knife holder and can be slid or pivoted into their protective position. All these finger guard mechanisms have the disadvantage that they provide no protection during the work phase because they have to be removed from the cutting edge region for use, in particular, for removing the section from the knife.
DE 198 24 024 A1 discloses a knife holder that has a pivotable blade guard constituted as a plate, wherein, in the protective position, the plate is disposed on the side of the knife facing away from the sample at a distance from the cutting edge of the knife such that access to the cutting edge is not possible. This bow-like pivotable blade guard can extend over the entire length of the knife and does not need to be removed for section removal. When access to the knife holder is required, e.g. to change the knife or to reposition the knife holder laterally, the blade guard can be swung out of its working position into its inoperative position. Then free access to the knife holder and operation of the clamping mechanisms are possible.
The disadvantage of this device is that the blade guard must be swung into position in addition to operating the knife holder. During the routine work that is performed with a microtome, in particular, each unnecessary operation is inconvenient for the user because it interferes with his or her work flow. This can result in the user preferring not to use the blade guard at all and operating the microtome without putting the blade guard in its protective position, which invalidates the function of the blade guard to reduce the risk of injury. Because routine work, in particular, is only performed by semi-skilled operators who cannot adequately assess the danger posed without having been trained in and practiced the necessary skills, but who have to work under time pressure, this results in a special hazard for laboratory personnel.
The objective is therefore to further develop a knife holder with a blade guard of the type stated above such that operability is improved and simplified, while also adequately ensuring safe operation for less skilled personnel.